The seven layers

Physical Layer The physical layer is the first layer that is responsible for the physical cable or wires connection between the network nodes.It defines the connector of the electrical cable ir wireless technology connecting the devices and it is responsible for the transmission of the raw data which is simply a series of the OS and 1s while taking care of a bit rate control. Data Link Layer The data link layer is the second layer that is responsible for establishing and terminating connections between two of the physically connected nodes on a network. It breaks up the packages into frames and sends them from the source of the destination. This layer is composed of two parts which are as follows: Logical Link Control that is used to identify network protocols that performs error checking and synchronized frames and Media Access Control that allows the connected devices to use MAC address to connect devices and define permissions to transmit and receive the data. Network layer The network layer is the third layer that is responsible for having two main functions. One is breaking up segments into network packets, and reassembling the packets on the receiving end. The other is routing packets by discovering the best path across a physical network. The network layer uses network addresses (typically Internet Protocol addresses) to route packets to a destination node. Transport layer The transport layer is the fourth layer that is responsible for taking data transferred in the session layer and breaking it into "segments" on the transmitting end. It is responsible for reassembling the segments on the receiving end, turning it back into data that can be used by the session layer. The transport layer carries out flow control,sending data at a rate that matches the connection speed of the receiving device, and error control, checking if data was received incorrectly and if not, requesting it again. Session layer The session layer is the fifth layer that is responsible for creating communication channels, called sessions, between devices. It is responsible for opening sessions,ensuring they remain open and functional while data is being transferred, and closing them when communication ends. The session layer can also set checkpoints during a data transfer--if the session is interrupted, devices can resume data transfer from the last checkpoint. Presentation layer The presentation layer is the sixth layer that is responsible for preparing data for the application layer. It defines how two devices should encode, encrypt, and compress data so it is received correctly on the other end. The presentation layer takes any data transmitted by the application layer and prepares it for transmission over the session layer. Application layer The application layer is the seventh layer which is the last layer that is responsible for being used by end-user software such as web browsers and email clients. It provides protocols that allow software to send and receive information and present meaningful data to users. A few examples of application layer protocols are the (HTTP), File Transfer Protocol (FTP), Post Office Protocol (POP), Simple Mail Transfer Protocol (SMTP), and Domain Name System (DNS).

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